The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Vehicles include an internal combustion engine that generates drive torque. More specifically, an intake valve is selectively opened to draw air into the cylinders of the engine. The air is mixed with fuel to form a combustion mixture. The combustion mixture is compressed within the cylinders and is combusted to drive pistons within the cylinders. An exhaust valve selectively opens to allow the exhaust gas to exit from the cylinders after combustion.
A rotating cam shaft regulates the opening and closing of the intake and exhaust valves. The camshaft includes a plurality of cam lobes that rotate with the camshaft. The profile of the cam lobe determines the valve lift schedule. More specifically, the valve lift schedule includes the amount of time the valve is open (duration) and the magnitude or degree to which the valve opens (lift). Manufacturers usually incorporate a fixed valve lift schedule for an engine since it may be suitable for a range of operating conditions. However, the fixed valve lift schedule may not be optimal during a particular engine operating condition. For example, during highway travel a vehicle may experience minimal acceleration. During such a condition, the engine may require less air per cylinder. However, when the engine operates on a fixed valve lift schedule excess air may be pumped into the engine cylinders, resulting in pumping losses of the engine.
A discrete variable valve lift (DVVL) system enables the engine to operate on more than one valve lift schedule. More specifically, a DVVL engine system switches between different valve lift schedules based on the operating conditions of the engine. This has been shown to minimize pumping losses of the engine.
A malfunction of the DVVL system may occur when a cylinder experiences differential valve lift. More specifically, differential valve lift occurs when a set of intake and/or exhaust valves of a particular cylinder operate on different valve lift schedules. In other words, the intake and/or exhaust valves of the cylinder are not synchronized. For example, a malfunction may occur when the DVVL engine system is operating in a high lift (HL) mode and one of the cylinders has an intake valve operating in a low lift (LL) mode and the other intake valve is operating in high lift (HL) mode.